DE69125748T2 - Liquid developer with hardenable liquid carrier materials - Google Patents

Description

The present invention is directed to liquid developer compositions suitable for the development of electrostatic latent images. In particular, the present invention is directed to liquid developers with curable, liquid binders.

Curable printing inks are known in the printing industry. For example, US-A-4,680,368 (Nakamoto et al.) discloses an ultraviolet curable printing ink composition comprising a polyurethane polymethacrylate prepared by reacting a polyisocyanate compound of the formula

wherein R₁ represents a hydrogen atom or a methyl group and n represents an integer of 1 to 20, with a hydroxyl group-containing methacrylate having in one molecule at least two methacryloyl groups and at least two urethane bonds, a radically polymerizable low molecular weight compound and a photopolymerization initiator.

In addition, US-A-4,443,495 (Morgan et al.) discloses a thermosetting conductive ink comprising (1) an ethylenically unsaturated radical selected from the group consisting of (a) a liquid, ethylenically unsaturated monomer, oligomer or prepolymer of the formula

(CH₂=- -O-)n-R₁

in which R is H or CH₃, R₁ is an organic radical and n is at least 2, (b) a polythiol in combination with (a), a polythiol in combination with a liquid, ethylenically unsaturated monomer, oligomer or prepolymer of the formula

in which R₂ is H or CH₃, R₃ is an organic radical and n is at least 2, and (d) mixtures of (a), (b) and (c), (2) a thermal initiator and (3) an electrically conductive material. Heating the composition in a desired pattern on a substrate yields a printed electrical circuit.

Furthermore, US-A-4,751,102 (Adair et al.) discloses a radiation-curable ink composition comprising a pigment and a photocurable composition, the photocurable composition comprising a free radical addition polymerizable or crosslinkable compound and a reactive counterion compound of an ionic dye capable of absorbing photochemically active radiation and generating free radicals which initiate free radical polymerization or crosslinking of the polymerizable or crosslinkable compound.

In addition, US-A-4,334,970 (Lombardi et al.) discloses a photosensitive resin system that is essentially solvent-free and contains an ester prepared from an unsaturated organic acid and a polyhydroxyl-containing material, a photoinitiator, a carbonyl initiator, a monomer capable of reacting with an acrylic monomer, and an unsaturated hydroxyl-containing hydrocarbon polymer. Furthermore, "Photochemical Aspects of UV Curing", Y.C. Chang, Photographic Science and Engineering, Vol. 21, No. 6 (1977) discloses the electro-optical properties of UV curing materials, the effect of pigment dispersion on the curing rate of printing inks containing pigments, and the spectroscopic calibration of the degree of UV curing.

US-A-3,661,614, US-A-4,003,868 and US-A-4,215,167 also disclose ultraviolet-curable printing inks.

US-A-4,399,209 (Sanders et al.) discloses a transfer imaging system in which images are formed by imagewise exposure of a layer comprising a dye-forming material and pressure-cleavable capsules containing as an internal phase a photosensitive composition. When a coated composition containing the dye-forming material and the encapsulated photosensitive composition is exposed to photochemically active rays and the capsules are subsequently cleaved in the presence of a developer, the image-forming reaction occurs between the dye-forming material and the developer, distinguishable in the exposed or unexposed areas, and produces a detectable image. This result is achieved by controlling whether the dye-forming material can be transferred from the imaging sheet to the developing sheet. In general, the photosensitive composition has a viscosity which changes upon exposure to photochemically active radiation in such a way that upon exposure a change in the viscosity of the internal phase in the exposed areas occurs, which imagewise determining whether the dye-forming material is accessible to the developer. The photosensitive composition may be a radiation-crosslinkable composition which increases in viscosity upon exposure to light and immobilizes the dye-forming material, thereby preventing transfer to the developer sheet and reaction with the developer material. Alternatively, the dye-forming material may be encapsulated with a substance which depolymerizes or otherwise decreases in molecular weight upon exposure, resulting in a decrease in viscosity, making the dye-forming material accessible or transferable in the exposed areas on the developer.

Liquid developers and liquid development processes for the development of electrostatic latent images are also known. In electrophoretic developers and processes, liquid developers generally comprise a liquid binder and colored toner particles, and often also contain a charge control agent. The colored toner particles become charged and upon contact of the electrostatic latent image with the liquid developer, the particles migrate through the liquid binder onto the charged image, causing development. Any residual liquid binder remaining on the image after development is evaporated or absorbed into the receiver sheet. Typically, liquid developers use liquid hydrocarbon binders, most commonly high boiling aliphatic hydrocarbons, which have a fairly high resistivity and are nontoxic. Developers and processes of this type are described, for example, in US-A-4,476,210, US-A- 2,877,133, US-A-2,890,174, US-A-2,899,335, US-A-2,892,709, US-A-2,913,353, US-A-3,729,419, US-A-3,841,893, US-A-3,968,044, US-A-4,794,651, US-A-4,762,764, US-A-4,830,945, US-A- 4,686,936, US-A-4,766,049, US-A-4,707,429, US-A-4,780,388, US-A-3,976,808, US-A-4,877,698, US-A-4,880,720 and US-A-4,880,432.

In polarizable liquid development processes described in US-A-3,084,043 (Gundlach), liquid developers having a relatively low viscosity and volatility and relatively high electrical conductivity (relatively low volume resistivity) are deposited on a gravure roller to fill the recesses on the roller surface. The excess developer is removed from the areas between the recesses and as a receiving surface charged in the image configuration passes near the gravure roller, the liquid developer is drawn from the recesses to the receiving surface by the charged image in the image configuration. Developers and processes of this type are described, for example, in US-A-4,407,943, US-A- 4,059,444, US-A-4,822,710, US-A-4,804,601, US-A-4,766,049, CA- A-937,823, CA-A-926,182, CA-A-942,554, GB-B-1,321,286 and GB-B-1,312,844.

In photoelectrophoretic liquid development processes, such as those described in US-A-4,135,925, US-A-3,383,993, US-A-3,384,488, US-A-3,384,565, US-A-3,384,566, US-A-4,043,655 and US-A-4,023,968, colored, photosensitive toner particles are suspended in an insulating carrier liquid. The suspension is placed between at least two electrodes subject to a potential difference and exposed to a light image. Typically, the imaging suspension is coated on a transparent, electrically conductive support in the form of a thin film and exposure is carried out through the transparent support while a biased second electrode is rolled over the suspension. It is believed that the particles carry an initial charge once suspended in the liquid carrier, causing them to be attracted to the transparent base electrode during the application of the potential difference. Upon exposure, the particles change polarity by exchanging charge with the base electrode, so that the exposed particles migrate to the second or roller electrode, forming images on each of the electrodes. by particle subtraction, each image being complementary to the other. Both polychromatic and monochromatic images can be formed by these processes. When polychromatic images are produced, the liquid developer can contain toner particles of more than one color.

Liquid developers containing curable resins in a liquid binder such as an aliphatic hydrocarbon are also known, as described, for example, in "Ultra-Violet Curable Liquid Immersion Development Toner", C.C. Chow, Xerox Disclosure Journal, Vol. 1, No. 5 (1976), Japanese Patents 62-115 171, 62-018 575, 62-018 574, 61-156 264, 61-156 263, 61-156 262, 61-156 261, 61-060 714, 63-155 055 and 62-089 364, additionally US-A-4,764,447, and Japanese Patents 62-007 718, 62-007 717, 62-007 716, 62-004 714, 61-020 056 and 60-249 156 disclose processes for the polymerization of monomers in a liquid hydrocarbon binder, forming dispersions of the polymer particles suitable for use as a liquid developer. Furthermore, Japanese Patent 62-014168 discloses an encapsulated toner contained in a liquid binder. The capsule core can be cured by heat and the monomers or oligomers are fixed to the paper when the images developed with the developer are cured.

A difficulty that often occurs when using electrophoretic liquid developers is an unpleasant odor that typically accompanies the liquid development processes. The sources of this odor are solvent vapors emitted by the copier or printer and the slow release of vapor from the residual liquid binder left on the recording film. A file drawer containing several documents produced by liquid development processes can accumulate vapor to an intolerable level. Accordingly, The reduction of solvent vapour emissions from liquid processing equipment and from prints produced with liquid developers is highly desirable for environmental and aesthetic reasons.

Although known materials are suitable for the intended purposes, there is a continuing need for liquid developer compositions that produce prints with little or substantially no odor. There is also a need for liquid developer compositions that reduce or substantially eliminate the emission or discharge of solvent vapors from copiers and printers using the liquid development processes. There is also a need for liquid developer compositions that have a curable liquid binder and enable the formation of high quality images. In addition, there is a need for liquid developers and liquid development techniques that reduce or eliminate the need to remove solvents from a copier or printer using liquid development. There is also a need for liquid developers and liquid development processes that enable the formation of images with excellent fixation to a support. In addition, there remains a need for liquid developers and liquid development processes that allow for simplified containment and capture processes to reduce or eliminate solvent emissions for copiers or printers used in liquid development.

It is an object of the present invention to satisfy at least some of the needs.

The present invention provides a liquid developer comprising a colorant and a substantial amount of a curable liquid binder having a resistivity of not less than about 10⁸ ohm cm and a viscosity of not more than about 500 centipoise (1 cP =1 mPas), wherein at least about 80% by weight of the liquid component of the developer comprises the curable liquid. The present invention also provides an electrophoretic liquid developer comprising a substantial amount of a curable liquid vehicle having a resistivity of less than about 5*10⁹ ohm cm and a viscosity of no more than about 20 centipoise, a charge control agent, and colored particles that can be charged and migrate through the liquid vehicle to develop an electrostatic latent image. More specifically, in this aspect of the invention, the liquid vehicle can have a viscosity of no more than about 3 centipoise and/or a resistivity of less than about 10¹⁰ ohm cm. The present invention further provides a liquid developer comprising a colorant and a substantial amount of a curable liquid vehicle having a resistivity of about 10⁸ to about 10¹¹ ohm cm and a viscosity of about 25 to about 500 centipoise. More specifically, in this aspect of the invention, the liquid binder may have a viscosity of about 30 to about 300 centipoise and/or a resistivity of about 2*10⁹9 to about 10¹⁰ ohm cm.

According to yet another aspect of the present invention, there is provided a photoelectrophoretic liquid developer comprising a substantial amount of a curable liquid binder having a resistivity of not less than about 109 ohm cm and a viscosity of not more than about 20 centipoise and photosensitive colored particles. More specifically, in this aspect of the invention, the liquid binder may have a viscosity of not more than about 3 centipoise and/or a resistivity of not less than about 1010 ohm cm. The developer may contain photosensitive colored particles of at least two different colors.

The present invention also provides a process comprising forming an electrostatic latent image, developing the image with an electrophoretic liquid developer comprising a substantial amount of a curable liquid binder having a viscosity of not more than about 20 centipoise and a resistivity of not less than about 5*10⁹ ohm cm, a charge control additive, and colored particles capable of being charged and migrating through the liquid binder, and curing the liquid binder remaining on the developed image after development. Curing can occur at any time before or after transfer of the developed image to a support. Transfer to a support is optional, and imaging and development can occur on a support, for example, when using direct marking imaging techniques.

The present invention further provides a method comprising forming an electrostatic image on an imaging member, providing an applicator having raised and depressed areas, applying a liquid developer comprising a colorant and a substantial amount of a curable liquid binder having a resistivity of from about 108 to about 1011 ohm cm and a viscosity of from about 25 to about 500 centipoise to the depressed areas of the applicator, contacting the raised portions of the applicator with the imaging member, causing the image to draw the developer from the depressed portions of the applicator to the latent image, developing the image, and curing the liquid binder remaining on the developed image.

According to yet another aspect of the present invention, a method is provided which comprises introducing a liquid developer containing a substantial amount of a curable, liquid vehicle having a resistivity of not less than about 5*10⁹ ohm cm and a viscosity of not more than about 20 centipoise and photosensitive colored particles, between at least two electrodes, exposing the developer between the electrodes to a light image while applying a potential between the electrodes, thereby causing the formation of an image by depositing the suspended particles in imagewise configuration on the electrodes, and curing the liquid vehicle remaining on the developed image.

The liquid vehicle in a developer according to the present invention can be any suitable liquid having the desired resistivity and viscosity properties which can be cured to form a solid. If the liquid developer is to be used in electrophoretic or photoelectrophoretic development systems, the liquid vehicle must be capable of allowing the colored toner particles of the developer to migrate through the vehicle to develop electrostatic latent images. Therefore, in electrophoretic and photoelectrophoretic developers, the liquid vehicle is sufficiently high in resistivity to favor development of the particles over development of the free ions which typically have a resistivity of greater than 5*10⁹ ohm cm, preferably greater than about 10¹⁰ Ohm cm, measured by determining the average current flow across a 1.5 mm gap at 5 hertz and 5 volts applied square wave potential.

In addition, the liquid vehicle is sufficiently low in viscosity to allow the toner particles to migrate toward the electrostatic latent image with sufficient velocity to enable development of the image within the desired development time. Typically, the liquid vehicle has a viscosity of not more than about 20 centipoise at the operating temperature of the copier or printer, preferably not more than about 3 centipoise at the operating temperature of the device.

When the liquid developer is to be used in a polarizable liquid development system, the liquid developer is applied to an applicator such as a gravure roller and brought into proximity with an electrostatic latent image. The charged image polarizes the liquid developer in the recesses in the applicator, thereby drawing the developer from the recesses and causing it to flow onto the image-bearing member, developing the image. For this use, the liquid vehicle of the liquid developer is somewhat more viscous than in the electrophoretic development situation because particle migration within the developer is generally not necessary and because the liquid developer must be sufficiently viscous to remain in the recesses in the applicator prior to development. However, the viscosity remains considerably lower than the viscosity typically observed for many printing inks because the liquid developer must be capable of being drawn from the recesses in the applicator roller by the force exerted by the electrostatic latent image. Therefore, liquid developers for use in polar development systems typically have a viscosity of about 25 to 500 centipoise at the operating temperature of the copier or printer, preferably about 30 to about 300 centipoise at the operating temperature of the machine. In addition, liquid developers to be used in polarizable liquid development systems typically have a resistivity lower than liquid developers used in electrophoretic or photoelectrophoretic development systems, thereby allowing the developer to become polarized upon entering the vicinity of the electrostatic latent image. However, liquid developers according to the present invention generally have resistivities which are considerably higher than the resistivities of typical printing inks, for which the resistivities are generally substantially less than about 10⁹9 ohm cm. Typically, liquid developers for polarizable liquid development systems have a resistivity of from about 10⁸ to about 10¹¹ ohm cm, and preferably from about 2x10⁹9 to about 10¹⁰ ohm cm.

Typical liquids suitable as a curable liquid binder include ethylenically unsaturated compounds, including monomers, dimers or oligomers having one or more ethylenically unsaturated groups, such as vinyl or allyl groups, and polymers having a terminal ethylenic double bond or ethylenic unsaturation in the side chain. Examples of suitable curable liquids include, but are not limited to, acrylate or methacrylate monomers or polymers containing acrylic or methacrylic groups of the general structure

wherein R₁ is H or CH₃. The active group may be attached to an aliphatic or aromatic group having from 1 to about 20 carbon atoms, preferably from about 8 to about 12 carbon atoms, to an aliphatic or aromatic siloxane chain or ring having from 1 to about 20 dimethylsiloxane units, to a combination of the above groups, or to a polymer chain. Examples of such compounds include n-dodecyl acrylate, n-lauryl acrylate, methacryloxypropylpentamethyldisiloxane, methylbis(trimethylsiloxy)silylpropylglycerol methacrylate, bis(methacryloxybutyl)tetramethyldisiloxane, 2-phenoxyethyl acrylate, polyethylene glycol diacrylate, ethoxylated bisphenol- A-diacrylate, pentaerythritol triacrylate, poly(acryloxypropylmethyl)siloxane, methacrylate terminated polystyrene, polybutyldiene diacrylate, etc. Other examples of curable fluids believed to be suitable include acrylic and methacrylic acid esters of polyhydric alcohols such as trimethylolpropane, pentaerythritol, etc., and acrylate or methacrylate terminated epoxy resins, acrylate or methacrylate terminated polyesters, etc. Another polymerizable material is the reaction product of epoxidized soybean oil and acrylic or methacrylic acid as described in US-A-4,215,167, as well as the urethane and amine derivatives described therein. Other examples of radiation curables include acrylic prepolymers derived from the partial reaction of pentaerythritol with acrylic acid and acrylic acid esters, including those available from the Richardson Company, Melrose Park, IL. Also believed to be suitable are the isocyanate modified acrylate, methacrylate and itaconic esters of polyhydric alcohols described in U.S. Patent Nos. 3,783,151, 3,759,809 and 3,825,479. Radiation curable compositions based on these isocyanate modified esters, which include reactive diluents such as tetraethylene glycol diacrylate, as well as photoinitiators such as chlorinated resins, chlorinated paraffins and amine photoinitiator synergists, are commercially available from Sun Chemical Corporation under the trade name "Suncure". Also, mixtures of pentaerythritol acrylate and halogenated, aromatic, alicyclic or aliphatic photoinitiators described in US-A-3,661,614 as well as other halogenated resins that can be crosslinked by ultraviolet irradiation are believed to be suitable. In addition, materials believed to be suitable are described in US-A-4,399,209.

Also suitable are epoxy monomers or epoxy-containing polymers with one or a plurality of functional Epoxy groups, such as the resins resulting from the reaction of bisphenol A (4,4'-isopropylidenediphenol) and epichlorohydrin or by the reaction of low molecular weight phenol-formaldehyde resins (novolak resins) with epichlorohydrin alone or in combination with an epoxy-containing compound as a reactive diluent. Reactive diluents such as phenyl glycidyl ether, 4-vinylcyclohexene dioxide, limonene dioxide, 1,2-cyclohexane oxide, glycidyl acrylate, glycidyl methacrylate, styrene oxide, allyl glycidyl ether, etc. can be used as viscosity modifiers. In addition, the range of these compounds can be expanded to include polymeric materials containing terminal epoxy groups or epoxy groups in the side chain. Examples of these compounds are vinyl copolymers containing glycidyl acrylate or methacrylate as one of the comonomers. Other classes of epoxy-containing polymers which are amenable to curing using the above catalysts are epoxysiloxane resins, epoxypolyurethanes and epoxypolyesters. Further examples of suitable epoxy resins are described in Encyclopedia of Polymer Science and Technology, 2nd Edition, Wiley Interscience, New York, pp. 322 to 382 (1986) and in Methods of Organic Chemistry, Vol. E20 Part 3, Georg Thieme Verlag Stuttgart, New York, pp. 1891 to 1994 (1987).

Other examples of suitable curable materials include vinyl ether monomers, oligomers or polymers containing vinyl ether groups of the general formula

CHR₁=CR₂-O-

in which R₁ and R₂ represent a hydrogen atom or alkyl radicals having from 1 to about 10 carbon atoms, and preferably from 1 to 2 carbon atoms. Examples of such materials include decyl vinyl ether, dodecyl vinyl ether, hexadecyl vinyl ether, 4-chlorobutyl vinyl ether, cyclohexyl vinyl ether, 1,4-cyclohexanedimethanol divinyl ether, diethylene glycol divinyl ether, Butanediol divinyl ether, hexanediol divinyl ether, octanediol divinyl ether, decanediol divinyl ether. Further examples of vinyl ether monomers and polymers are in "Synthesis, Characterization, and Properties of Novel Aromatic Bispropenyl Ether" by JV Crivello and DA Conlon, Journal of Polymer Science: Polymer Chemistry Edition, Vol. 22, 2105-2121 (1984), "Aromatic Bisvinyl Ethers: A New Class of Highly Reactive Thermosetting Monomers" by JV Crivello and DA Conlon, Journal of Polymer Science: Polymer Chemistry Edition, Vol. 21, 1785-1799 (1983), "Vinyloxy-Functional Organopolysiloxane Compositions", by JV Crivello and RP Eckberg, US-A- 4,617,238, "Carbocationic Polymerization of Vinyl Ethers" by T. Higashimura, M. Sawamoto in Comprehensive Polymer Science, Vol. 3, pp. 673 to 696 (1989). "Polymerization of vinyl ethers" by J. Reiners in Methods of Organic Chemistry, Vol. E20, Part 2, Georg Thieme Verlag Stuttgart, New York, pp. 1071-1115 (1987). Cyclic vinyl ethers with the following basic structure.

wherein R1 is hydrogen or an alkyl group having from 1 to about 20 carbon atoms, preferably from 1 to about 4 carbon atoms, and n is from 2 to about 20, preferably from 3 to 8, such as 4-phenyl-2-methylenetetrahydrofuran, 2-methylene-3,4-benzotetrahydrofuran, 2,2'-diphenyl-4-methylene-1,3-dioxolane, 2-methyl-2-phenyl-4-methylene-1,3-dioxolane, etc., are also useful. Further examples can be found in "Ring-Opening Polymerization" by W.J. Bailey in Comprehensive Polymer Science, Vol. 3, pp. 283-320 (1989).

Also suitable are styrene and indene monomers or oligomers and polymers containing styrene or indene groups of the general formula

in which R₁ and R₂ are hydrogen, alkyl or aromatic, X is an electron donating group such as alkyl, alkoxy, N,N-dialkylamine, etc. The styrene and indene moieties shown above may be bonded to a polymer chain. Examples of such materials include butylstyrene, p-ethoxystyrene, p-butoxystyrene, p-octoxystyrene, o-allyloxystyrene, divinylbenzene, 1,4-bis(p-vinylbenzeneoxy)butane, 1,8-bis(p-vinylbenzeneoxy)octane, etc. Further examples of styrene and indene monomers are given in Vinyl and Related Polyers, by C.E. Schildknecht, Wiley and Sons, 1952, Chapters 1, 2 and 3 and Cationic Polymerization of Olefins: A Critical Inventory, by J.P. Kennedy, Wiley and Sons 1975, pp. 228-330.

In addition, vinyl acetal and ketene acetal monomers of the general formulas

in which R₁ is a hydrogen atom or alkyl radicals or aromatic radicals having 1 to about 20 carbon atoms and preferably 1 to about 6 carbon atoms and R₂ and R₃ are alkyl radicals or aromatic radicals having from 1 to about 20 carbon atoms and preferably from 1 to about 6 carbon atoms, n is 2 to 20 and preferably 3 to 8, as in the case of the cyclic vinyl acetal (II). Typical examples include diethyl ketene acetal, dibutyl ketene acetal, diphenyl ketene acetal, 2-methylene-1,3-dioxepane, 4-phenyl-2- methylene-1,3-dioxepane, 4,6-dimethyl-2-methylene-1,3-dioxane, 2-methylene-1,3-diox-5-ene, 4-vinyl-2-methylene-1,3-dioxolane, etc. Further examples are described in "Ring-Opening Polymerization" by WJ Bailey in Comprehensive Polymer Science, Vol. 3, pp. 283-320 (1989).

Furthermore, linear or branched aliphatic α-olefins, such as 1-dodecene, 5-methyl-1-heptene, 2,5-dimethyl-1,5-hexadiene, etc., alicyclic olefins and diolefins, such as d-limonene, 1-4- dimethylenecyclohexane, 1-methylene-4-vinylcyclohexane, etc., conjugated polyenes, such as 2-phenyl-1,3-butadiene, myrcene, allocimene, 1-vinylcyclohexene, ethylbenzofulvene, etc., bicyclic olefins, such as α-pinene, β-pinene, 2-methylenenorbornane, etc., are all suitable carrier liquids. Furthermore, further examples of this class of olefins are described in Cationic Polymerization of Olefins: A Critical Inventory, by J.P. Kennedy, Wiley and Sons, pp. 1 to 228 (1975).

Liquid 1,2-polybutadiene resins of the formula

-[CH₂-CH-(CH=CH₂)]n

having a molecular weight between about 200 and about 3000, and preferably between about 200 and 1000 are also suitable. A thiol compound is generally present as the comonomer with the olefin monomers. Typical examples include trithioltrimethylolethane tris(β-mercaptopropionate), tetrathiolpentaerythritol tetrakis(thioglycolate), dimonene dimercaptan, etc.

Other curable liquid materials include those containing residues such as cinnamic acid groups of the formula

- -CH=CH-

Fumaric or maleic acid groups of the formula

- -CH=CH- -

or maleimide groups of the formula

contain.

These functional groups can be present either within a monomer or a polymer comprising the liquid.

Specific examples include citral, cinnamic acid acetate, cinnamaldehyde, 4-vinylphenyl cinnamate, 4-vinylphenyl 4-nitrocinnamate, 4-isopropenylphenyl cinnamate, poly[1-(cinnamoyloxymethylphenyl)ethylene], poly{1-(cinnamoyloxymethylphenyl)ethylene-co-1-[(4-nitrophenoxy)methylphenyl]ethylene}, 3-(2- furyl)acrolein), diethyl fumarate, dihexyl fumarate, dibutyl maleate, diphenyl maleate, N- phenylmaleimide, N-(4-butylphenyl)maleimide, m-phenylenediaminebis(maleimide) and N,N'-1,3-phenylenedimaleimide and polyfunctional maleimide polymer MP-2000 from Kennedy and Klim Little Silver, NJ.

In addition, monomers, dimers or oligomers containing a plurality of one or more suitable functional groups can also be used as the curable liquid.

If desired, the curable liquid may contain a cross-linking agent. Cross-linking agents are generally monomers, dimers or oligomers that contain a variety of functional groups such as two styrene functionalities, one styrene functionality and one acrylate functionality, or the like. The curable liquid may consist entirely of these multifunctional monomers, dimers or oligomers, may contain no crosslinking agent at all, and may contain both monofunctional monomers, dimers or oligomers and multifunctional monomers or oligomers. In general, the presence of a crosslinking agent is preferred to provide improved film forming properties, faster curing, and improved adhesion of the cured image to the support. When present, the crosslinking agent is present in an effective amount, typically from about 1 to about 100% by weight of the curable liquid, preferably from about 10 to 50% by weight of the curable liquid.

Liquid developers according to the present invention may also contain an initiator to initiate curing of the liquid binder. The initiator may be added before or after development of the image. Any initiator may be used: examples of the types of initiators that are suitable include thermal initiators, radiation-sensitive initiators such as ultraviolet initiators, infrared initiators, visible light initiators or the like, initiators that are sensitive to electron radiation, ion radiation, gamma radiation or the like. In addition, combinations of initiators from one or more classes of initiators may be used. Radical photoinitiators and thermal radical initiators are well known, as is electron beam curing. These materials and processes are described, for example, in "Radiation Curing of Coatings", GA Senich and RE Florin, Journal of Macromolecular Science Review. Macromol. Chem. Phys. C24 (2), 239-324 (1984). Examples of initiators include those that generate radicals by direct photofragmentation, including benzoin ethers such as benzoin isobutyl ether, benzoin isopropyl ether, benzoin methyl ether, etc., acetophenone derivatives such as 2,2-dimethoxy-2- phenylacetophenone, dimethoxyacetophenone, 4-(2-hydroxyethoxy)phenyl(2-propyl)ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 2,2,2-trichloroacetophenone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, etc. Initiators that form radicals by bimolecular hydrogen transfer, such as the photoexcited triplet state of diphenyl ketone or benzophenone, diphenoxybenzophenone, bis(N,N-dimethylphenyl)ketone or Michler's ketone, anthraquinone, 4-(2-acryloyloxyethoxy)phenyl-2-hydroxy-2-propylketone and other similar aromatic carbonyl compounds, etc., Initiators that form radicals by electron transfer or via a donor acceptor complex also known as an exiplex, such as methyldiethanolamine and other tertiary amines, Photosensitizers that in combination with a Free radical generating initiators wherein the sensitizer absorbs light energy and transfers it to the initiator, such as a combination of a thioxanthone sensitizer and a quinolinesulfonyl chloride initiator and similar combinations, cationic initiators which decompose upon light to strong Lewis acids, such as aryldiazonium salts of the general formula Ar-N₂X, wherein Ar is an aromatic ring such as butylbenzene, nitrobenzene, dinitrobenzene or the like and X is BF₄, PF₆, AsF₆, SbF₆, CF₃SO₃; or the like, diaryliodonium salts represented by the general formula Ar₂IX wherein Ar represents an aromatic ring such as methoxybenzene, butylbenzene, butoxybenzene, octylbenzene, didecylbenzene or the like, and X represents an ion having a low nucleophilicity such as PF₆, AsF₆, BF₄, SbF₆, CF₃SO₃, etc., triarylsulfonium salts represented by the general formula Ar₃SX wherein Ar represents an aromatic ring such as hydroxybenzene, methoxybenzene, butylbenzene, butoxybenzene, octylbenzene, dodecylbenzene or the like, and X represents an ion having a low nucleophilicity such as PF₆, AsF₆, SbF₆, BF₄, CF₃SO₃ or similar means non-radical initiators, which include amine salts of α-ketocarboxylic acids, such as the tributylammonium salt of phenylglyoxylic acid, etc., as well as mixtures thereof. Furthermore, acid generating photoinitiators are described in "The Chemistry of Photoacid Generating Compounds" by JV Crivello in Proceedings of the ACS Division of Polymeric Materials. Science and Engineering, Vol. 61, pp. 62-66 (1989), "Redox Cationic Polymerization: The Diaryliodonium Salt/Ascorbate Redox Couple", by JV Crivello and JHW Lam in Journal of Polymer Science: Polymer Chemistry Edition, Vol. 19, pp. 539-548 (1981), "Redox- Induced Cationic Polymerizatizon: The Diaryliodonium Salt/Benzoin Redox Couple", by JV Crivello and JL Lee in Journal of Polymer Science: Polymer Chemistry Edition, Vol. 21, pp. 1097-1110 (1983) "Diaryliodonium Salts as Thermal Initiators of Cationic Polymerization", by JV Crivello, TP Lockhart and JL Lee in Journal of Polymer Science: Polymer Chemistry Edition, Vol. 21, pp. 97-109 (1983).

Further examples of suitable initiators include α-alkoxyphenyl ketones, O-acylated α-oximino ketones, polycyclic quinones, xanthones, thioxanthones, halogenated compounds such as polynuclear aromatic chlorosulfonyl and chloromethyl compounds, heterocyclic chlorosulfonyl and chloromethyl compounds, chlorosulfonyl and chloromethyl benzophenones and fluorenones, haloalkanes, α-halo-α-phenylacetophenone, photoreducible dye reducing agent redox couplers, halogenated paraffins such as brominated or chlorinated paraffin, benzoin alkyl esters, cationic diborate anion complexes, anionic diiodonium ion compounds and anionic dye pyrrilium compounds.

Additional examples of suitable initiators are given, for example, in US-A-4,683,317, US-A-4,378,277, US-A-4,279,717, US-A- 4,680,368, US-A-4,443,495, US-A-4,751,102, US-A-4,334,970, "Complex Triarylsulfonium Salt Photoinitiators I. The Identification, Characterization, and Syntheses of a New Class of Triarylsulfonium Salt Photoinitiators", JV Crivello and JHW Lam, Journal of Polymer Science: Polymer Chemistry Edition, Vol. 18, 2677-2695 (1980); "Complex Triarylsulfonium Photoinitiators II. The Preparation of Several New Complex Triarylsulfoniun salts and the Influence of Their Structure in Photoinitiated Cationic Polymerization", JV Crivello and JHW Lam, Journal of Polymer Science Polymer Chemsitry Edition, Vol. 18, pp. 2697-2714 (1980); "Diaryliodonium Salts A New Class of Photoinitiators for Cationic Polymerization", JV Crivello and JHW Lam, Maromolecules, Vol. 10, pp. 1307-1315 (1977); and "Developments in the Design and Applications of Novel Thermal and Photochemical Initiators for Cationic Polymerization" by JV Crivello, JL Lee and DA Conlon in Makromol. Chem. Macromolecular Symposium, Vol. 13/14, pp. 134-160 (1988). The initiator is present in the curable liquid in an effective amount of generally from about 0.1 to about 10% by weight of the liquid, and preferably from about 0.1 to 3% by weight of the liquid.

If a photoinitiator is selected, photopolymerization can be carried out using an autoxidant, which is generally a compound capable of consuming oxygen in a free radical chain process. Examples of useful autoxidizing agents include N,N-dialkylanilines, particularly those substituted in one or more of the o-, m- or p-positions with groups such as methyl, ethyl, isopropyl, t-butyl, 3,4-tetramethylene, phenyl, trifluoromethyl, acetyl, ethoxycarbonyl, carboxy, carboxylate, trimethylsilylmethyl, trimethylsily, triethylsilyl, trimethylgermanyl, triethylgermanyl, trimethylstannyl, triethylstannyl, n-butoxy, n-pentyloxy, phenoxy, hydroxy, acetyloxy, methylthio, ethylthio, isopropylthio, thio(mercapto), acetylthio, fluorine, chlorine, bromine or iodine. Auto-oxidizing agents, when present, are present in an effective amount of typically about 0.1 to about 5% by weight of the curable liquid.

A UV sensitizer capable of providing electron transfer and exciplex-induced bond cleavage processes during radiation curing may optionally be included in a liquid developer according to the present invention. Typical photosensitizers include anthracene, perylene, phenothiazine, thioxanthone, benzophenone, fluorenone, etc. The sensitizer is in an effective Amount, typically from about 0.1 to about 5% by weight of the curable liquid.

A liquid developer according to the present invention may also comprise a charge control agent. A charge control agent will generally be present in electrophoretic liquid developers and photoelectrophoretic liquid developers to impart sufficient charge to the particles present in the liquid to enable them to migrate through the liquid vehicle to develop an image. Examples of suitable charge control agents for liquid developers include the lithium, cadmium, calcium, manganese, magnesium and zinc salts of heptanoic acid, the barium, aluminum, cobalt, manganese, zinc, cerium and zirconium salts of 2-ethylhexanoic acid (these are known as metalloctoates), the barium, aluminum, zinc, copper, lead and iron salts of stearic acid, the calcium, copper, manganese, nickel, zinc and iron salts of naphthenic acid and ammonium lauryl sulfate, sodium dihexyl sulfosuccinate, sodium dioctyl sulfosuccinate, aluminum diisopropyl salicylate, aluminum resinate, the aluminum salt of 3,5-di-t-butyl-γ-resorcylic acid. Mixtures of these materials may also be used. Particularly preferred charge control agents include lecithin (Fisher Inc.); OLOA 1200, a polyisobutylene succinimide available from Chevron Chemical Company, basic barium petronate (Witco Inc.), zirconium octoate (Nuodex), aluminum stearate, salts of calcium, manganese, magnesium and zinc with heptanoic acid, salts of barium, aluminum, cobalt, manganese, zinc, cerium and zirconium with octanoic acid, salts of barium, aluminum, zinc, copper, lead and iron with stearic acid, iron naphthenate, etc., as well as mixtures thereof. The charge control additive may be present in an amount of from about 0.001 to about 3%, and preferably from about 0.01 to about 0.8% by weight of the developer composition. Other additives such as charge aids added to improve the charging properties of the developer may be added to the developers. Charge aids such as stearates, metallic Soap additives, polybutylene succinimides, etc., are described in publications such as US-A-4,707,429, US-A-4,702,984 and US-A- 4,702,985.

In the liquid developer according to the present invention, the curable liquid component is present in a large amount and generally represents the weight percent of the developer not comprised by the solid components, although (as described below) a non-curable liquid component, e.g. a release agent, may also be present. The total amount of liquid binder present is at least 80% by weight of the developer and contains at least 80% by weight of the curable liquid.

A liquid developer according to the present invention may contain any type of colored toner particle typically used in conventional liquid developers and compatible with the liquid binder. For example, the toner particles may consist solely of pigment particles dispersed in the liquid binder. Since the liquid binder is cured to a solid before or after transfer, the pigment particles can be fixed to the printing substrate by the cured liquid binder and no additional polymer component in the developer is required for fixing purposes. However, if desired, a polymer component may be present in the developer. That is, in certain embodiments of the invention, the colored particles are pigment particles and the developer also contains a polymer. The polymer may be soluble in the liquid binder and may be polymers such as poly(2-ethylhexyl methacrylate), poly(isobutylene-co-isoprene) such as Kalen 800 available from Hardman Company, NJ, polyvinyltoluene based copolymers including vinyltoluene acrylic acid copolymers such as Pliolite OMS, Pliolite AC, Pliolite AC- L, Pliolite FSA, Pliolite FSB, FSD, Pliolite FSE, Pliolite VT, Pliolite VT-L, Pliolite VTAC and Pliolite VTAC-L available from Goodyear Tire and Rubber Company, Neocryl S-1002 and EX519 available from Polyvinyl Chemistry Industries, Parapol 900, Parapol 1300 and Parapol 2200 available from Exxon Company, etc., block copolymers such as poly(styrene-b-hydrogenated butadiene) including Kraton G 1701 available from Shell Chemical Company, etc., as well as mixtures thereof. Additionally, the polymer may be insoluble in the liquid binder and may be present either as separate particles or as an encapsulated shell around the pigment particles. That is, in certain embodiments of the present invention, the colored particles comprise pigment particles and a polymer. Examples of suitable polymers in this case include ethylene vinyl acetate copolymers such as Elvax-I resins available from EI Du Pont de Nemours & Company, copolymers of ethylene and an α,β-ethylenically unsaturated acid selected from acrylic or methacrylic acid, the acid residue being present in an amount of 0.1 to 20 wt.% such as Nucrel-II resins available from EI Du Pont de Nemours & Company, polybutyl terephthalates, ethylene ethyl acrylate, copolymers such as those available as Bakelite DPD 6169, DPDA 6182 Natural and DTDA 9169 Natural from Union Carbide Company, ethylene vinyl acetate resins such as DQDA 6479 Natural 7 and DQDA 6832 Natrual 7 available from Union Carbide Company, methacrylate resins such as polybutyl methacrylate, Polyethyl methacrylate and polymethyl methacrylate available under the trade name Elvacite from EI Du Pont de Nemours & Company, and other pigment particles described, for example, in GB-B-2,169,416 and US-A-4,794,651. Furthermore, the polymer may be partially soluble in the liquid solvent or soluble in the liquid solvent at elevated temperatures, for example above 75°C, and insoluble at ambient temperatures, for example about 10 to 65°C. Examples of suitable polymers in this case include polyolefins and halogenated polyolefins such as chlorinated polypropylenes and poly-α-olefins including polyhexadekenes and polyoctadekenes etc.

Suitable pigment materials include carbon black pigments such as Microlith CT available from BASF, Printex 140V available from Degussa, Raven 5250 and Raven 5720 available from Columbian Chemicals Company, and Mogul-L, Black Pearls L and Regal carbon black pigments from Cabot Corporation. The pigment materials may be colored and may include magenta pigments such as Hostaperm Pink E (Hoechst Celanese Corporation) and Lithol Scarlet (BASF), yellow pigments such as Diarylide Yellow (Dominion Color Company), cyan pigments such as Sudan Blue OS (BASF), etc. In general, any pigment material is suitable provided that it is small in particle size and that it either combines well with any polymeric material also included in the developer composition or is suitable as a toner particle in its own right by having the desired particle size and, in the electrophoretic and photoelectrophoretic embodiments of the present invention, is capable of being charged and migrating through the liquid vehicle to develop an image. The pigment particles are present in an amount sufficient to enable development of a colored image, typically from about 5 to about 100 percent by weight of the solids content of the developer. Polymeric components of the solids portion of the developers, when present, are present in any amount up to about 95 percent by weight of the solids content of the liquid developer.

Examples of photosensitive pigments suitable for use in photoelectrophoretic liquid developers according to the present invention are described, for example, in US-A-3,384,488. This patent also discloses additional materials, such as charge transfer materials, which may be present in photoelectrophoretic liquid developers according to the present invention.

In all cases where a pigment is a component of the liquid developer, the pigment may be a "flush pigment". "Flush pigments" are generally the pigments that are sold in a form suitable for ready dispersion into organic media. Pigments are often prepared by an aqueous precipitation reaction and the product collected in a water-wetted pigment cake by filtration. The cake is then dried to yield a dry pigment powder. "Flush pigments", however, are not dried to powder, but instead the filter cake is mixed with an organic solvent such as mineral oils, litho oils or gloss paint clear coats until phase transfer occurs in which the pigment is spontaneously transferred from the aqueous phase to the organic phase as a result of stirring. The use of "flush pigments" for developers according to the present invention provides advantages such as reduced need for mixing and processing of the liquid developer during formulation, while maintaining the desired pigment particle sizes since the particles are already small in the organic dispersion. In addition, the organic pigment dispersion can be easily mixed with a variety of binders. Particularly preferred for the developers according to the present invention are "flush pigments" in curable liquid media such as alkyds, polyesters or the like. A liquid developer according to the present invention can be prepared from the "flush pigments" by simply mixing the "flush pigment" with the liquid binder and the other developer ingredients. Examples of "flush pigments" suitable for the present invention include alkyd-based "flush pigments", Sunset II, Quantum Set II, Polyversyl and Valuset II "flush pigments" from Sun Chemical Corporation, etc. Further information regarding "flush pigments" is contained, for example, in US-A-4,794,066.

In addition, liquid developers according to the present invention may contain toner particles comprising colored silica particles.

Additional references disclosing suitable toner particles include US-A-4,794,651, US-A-4,762,764, US-A-3,729,419, US-A-3,841,893, and US-A-3,968,044.

In embodiments of the present invention, such as the liquid developers and processes using polarizable liquid development, the developer may contain a dye rather than pigment particles. Furthermore, in embodiments of the present invention in which colored particles migrate through the liquid medium to form images, the particles may be colored with a dye rather than a pigment. Suitable dyes include Orasol Blue 2GLN, Red G, Yellow 2 GLN, Blue GN, Blue BLN, Black CN, Brown CR, all available from Ciba-Geigy, Inc. Mississauga, Ontario, Morfast Blue 100, Red 101, Red 104, Yellow 102, Black 101, Black 108, all available from Morton Chemical Company, Ajax Ontario, Bismark Brown R, available from Aldrich, Neolan Blue, available from Ciba-Geigy, Savinyl Yellow RLS, Black RLS, Red 3 GLS, Purple GBLS, all available from Sandoz Company, Mississauga, Ontario, etc. The dyes are generally present in an amount of from about 5 to about 30% by weight of the toner particle, although other amounts may be present.

Liquid developers according to the present invention may also contain various polymers added to modify the viscosity of the developer or to modify the mechanical properties of the developed or cured image, such as adhesion or binding force. Particularly, when the liquid developer is to be used in polarizable liquid development processes, the developer may also comprise viscosity control agents. Examples of suitable viscosity control agents include thickeners such as alkylated polyvinylpyrrolidones such as Ganex V216 available from GAF, polyisobutylenes such as Vistanex available from Exxon Corporation, Kalene 800 available from Hardman Company, New Jersey, ECA 4600 available from Paramins, Ontario, etc., Kraton G-1701, a block copolymer of Polystyrene-b-hydrogenated butadiene available from Shell Chemical Company, Polypaleester 10, a glycol resin ester available from Hercules Powder Company, and other similar thickeners. Additionally, additives such as pigments, including silica pigments such as Aerosil 200, Aerosil 300, etc. available from Degussa, Benton 500, a treated montmorillonite clay available from NL Products, etc. may be included to achieve the desired developer viscosity. The additives are present in any effective amount, typically from about 1 to about 40 weight percent in the case of the thickeners and from about 0.5 to about 5 weight percent in the case of pigments and other particulate additives.

In addition, the liquid developers according to the present invention, which are to be used in polarizable liquid development processes, can also contain agents for improving conductivity. For example, the developers can contain additives such as quaternary ammonium compounds, which are described, for example, in US-A-4,059,444.

In a specific embodiment of the present invention, the liquid developers may contain a small amount of a release agent. Images formed with the developers may be cured before or after transfer of the image to a printing support. In addition, the images may be partially cured before transfer, followed by additional curing after transfer. When the image is cured before transfer, it is desirable for the image to be easily released from the imaging member and also adhere to the support, such as paper, a transparent material, or the like. By including a small amount of release agent in the developer, transfer from the imaging member is improved. Examples of suitable release agents include non-curable liquids typically used as liquid binders for liquid developers, such as high purity aliphatic hydrocarbons having, for example, about 7 to about 25 carbon atoms and preferably having a viscosity of less than 2 centipoise, such as Norpar 12, Norpar 13 and Norpar 15 available from Exxon Corporation, isoparaffinic hydrocarbons such as Isopar G, H, K, L, M and V available from Exxon Corporation, Amsco 460 solvent, Amsco OMS available from American Mineral Spirits Company, Soltrol available from Phillips Petroleum Company, Pagasol available from Mobil Oil Corporation, Shellsol available from Shell Oil Company, etc., as well as mixtures thereof. The release agent can be present in any amount up to about 20% by weight of the liquid. Curing or partially curing an image developed with a developer containing a noncurable release agent results in a coherent image which is readily released from the smooth imaging element but which still readily adheres to the support, particularly porous supports such as paper or fabrics. The uncured portion of the liquid is then absorbed into the carrier, particularly if that portion is a high molecular weight hydrocarbon such as Magiesol 60 or Isopar V or a silicone oil. Release agent functionality can also be obtained by using siloxane or fluorocarbon containing components in the curable binder. The liquid binder can either contain a siloxane or fluorocarbon release agent as an additive or, if the selected siloxane or fluorocarbon release agent has a suitable viscosity and resistivity, contain a major portion (up to 100% by weight) of the siloxane or fluorocarbon release agent. Examples of siloxane materials include 4-vinylcyclohexene oxide terminated polydimethylsiloxanes such as GE's UV9300 and UV9305 silicone epoxy polymers.

Liquid developers according to the present invention can generally be prepared according to any process suitable for the type of toner particles selected. For example, when the toner components comprise a polymer and a pigment, the developer can be prepared by mixing the ingredients followed by milling the mixture in an attritor in the presence of the selected liquid binder. When the toner ingredients comprise colored silica particles, the developer can be prepared by heating and mixing the ingredients followed by milling the mixture in an attritor until homogeneity of the mixture is achieved. Colored silica particles can be prepared according to the process described, for example, in US-A-4,566,908, US-A-4,576,888 and US-A-4,877,451. When the solids content of the developers includes pigment particles and a polymer which is soluble in the liquid binder at elevated temperatures and insoluble at room temperatures, the polymer can be dispersed by heating the mixture, milling the mixture in an attritor at elevated temperatures and milling while the mixture cools. Methods for preparing various types of liquid developers are described in several of the above-mentioned documents, including US-A-4,476,210, US-A-4,794,651, US-A-4,877,698, US-A-4,880,720 and US-A-4,880,432. The charge control agent can be added either during mixing of the other ingredients or after the developer has been prepared. Similarly, the initiator, which enables the liquid binder to harden, can be added either with the other developer ingredients or at a later time, including immediately before using the developer. Furthermore, in another embodiment of the present invention, the liquid developer contains little or no initiator during the development step and the initiator is added to the developed image. This can be achieved in any manner such as spraying the developed image with the starter, incorporating the starter into the support on which the final image is contained, applying the starter as a primer or topcoat, etc. In addition, the liquid developer may contain little or no crosslinking agent during the development step and the crosslinking agent may to the developed image in any appropriate manner.

In general, images are developed with electrophoretic liquid developers and polarizable liquid developers according to the present invention by forming an electrostatic latent image and contacting the latent image with the liquid developer, thereby causing the image to be developed. When an electrophoretic liquid developer is used, the method comprises forming an electrostatic latent image and contacting the latent image with the developer comprising a liquid binder and charged toner particles, thereby causing the charged particles to migrate through the binder and develop the image. Developers and processes of this type are described, for example, in US-A-4,804,601, US-A-4,476,210, US-A-2,877,133, US-A- 2,890,174, US-A-2,899,335, US-A-2,892,709, US-A-2-913,353, US-A-3,729,419, US-A-3,841,893, US-A-3,968,044, US-A-4,794,651, US-A-4,762,764, US-A-4,830,945, US-A-3,976,808, US-A- 4,877,698, US-A-4,880,720 and US-A-4,880,432. When a liquid developer suitable for polarizable liquid development processes is used, the process comprises forming an electrostatic latent image on an imaging member, applying the liquid developer to an applicator, and bringing the applicator into sufficient proximity to the latent image to cause the image to attract the developer to the imaging member, thereby developing the image. Developers and processes of this type are described, for example, in US-A-4,047,943, US-A-4,059,444, US-A-4,822,710, US-A-4,804,601, US-A-4,766,049, US-A-4,686,936, US-A-4,764,446, CA-B-937,823, CA-B-926,182, CA-B-942,554, GB-B-1,321,286 and GB-B-1,312,844. In both of these embodiments, any suitable means may be used to form the image. For example, a photosensitive imaging element may be exposed by means of incident light or by means of a laser to form a latent image on the element, followed by development of the image and transfer to a carrier such as paper, a transparent material, fabric or similar. In addition, an image can be formed on a dielectric imaging element by electrographic or ionographic processes, for example, as described in US-A- 3,564,556, US-A-3,611,419, US-A-4,240,084, US-A-4,569,584, US-A-2,919,171, US-A-4,524,371, US-A-4,619,515, US-A-4,463,363, US-A-4,254,424, US-A-4,538,163, US-A-4,409,604, US-A- 4,408,214, US-A-4,365,549, US-A-4,267,556, US-A-4,160,257 US-A-4,485,982, US-A-4,731,622, US-A-3,701,464 and US-A-4,155,093, followed by development of the image and optionally transfer to a support. Optionally, the transferred images can be fused to the support by any means such as heat, pressure, exposure to solvent vapor or sensitizing radiation such as ultraviolet light or the like, as well as combinations thereof. Furthermore, liquid developers according to the present invention can be used to develop electrographic images, wherein an electrostatic image is formed directly by electrographic or ionographic processes and then developed without subsequent transfer of the developed image to an additional support.

The photoelectrophoretic liquid developers of the present invention can be used in photoelectrophoretic development processes which generally comprise placing a suspension of electrically photosensitive particles in a liquid between two electrodes, at least one of which is generally a substantially transparent plate. Exposing the suspension to a light image while applying a field between the electrodes causes the formation of an image by deposition of the suspended particles in imagewise configuration on the electrode. In one process, for example, described in US-A-4,043,655, both electrodes are transparent plates. In another process, for example, described in US-A-4,023,968, one electrode is a transparent, conductive support and the other electrode is a generally cylindrically shaped biased electrode which is rolled over the first electrode onto which the suspension of photosensitive particles has been applied. Among other methods, multi-color images can be produced by using a developer containing photosensitive particles of all desired colors and sequentially exposing the suspension to light images through color filters. Photoelectrophoretic processes are described in detail in US-A-4,043,655, US-A-4,023,968, US-A-4,066,452, US-A-3,383,993, US-A-3,384,566, US-A-3,384,565 and US-A-3,384,488. The photoelectrophoretic liquid developers of the present invention can be prepared by preparing any of the photoelectrophoretic liquid developers described in these patents, except that the liquid binder is replaced by a curable liquid having the desired resistivity and viscosity properties.

Following development of an image with a liquid developer in accordance with the present invention, the image is cured, causing the residual liquid binder on the image to solidify. Curing may occur prior to transfer or after transfer. In situations such as electrographic imaging where the image is developed directly on the support and no transfer occurs, the image may be cured after development. If transfer to a support is desired, the developed image may be partially cured prior to transfer. Partial curing may impart surface adhesive properties to the developed image which may enhance transfer to a support. In addition, curing after transfer may greatly improve the adhesion of the image to the support since the liquid binder may penetrate into the support, particularly when the support, such as cloth or paper, is porous, and curing causes the image to be firmly bonded to the fibers of the support. In addition Post-transfer curing can greatly improve adhesion to the support, whether the support is smooth or porous, if the support has reactive sites that either occur naturally, such as in cellulose or clay, or that are added as a precoat with which the reactive species in the liquid developer can react.

Curing may be any suitable means and is generally determined at least in part by the nature of the initiator selected. If a photoinitiator is selected, curing is effected by exposing the image to radiation of the wavelength to which the initiator is sensitive, such as UV light. Examples of suitable ultraviolet lamps include low pressure mercury lamps, medium pressure mercury lamps, high pressure mercury lamps, xenon lamps, mercury xenon lamps, arc lamps, gallium lamps, lasers, etc. If a thermal initiator is selected, the image is heated to a temperature at which the initiator can initiate curing of the liquid binder and held at that temperature for a period of time sufficient to cure the image. Electron beam curing can be initiated by any electron beam device. Examples include scanned beam apparatuses in which the electrons are generated as a near point source and the precise beam electromagnetically scans the desired area, such as those available from High Voltage Engineering Corporation, Radiation Dynamics, Inc. (a subsidiary of Monsanto Company), Polymer Physik of Germany, or the like, and linear-filament apparatuses or curtain processor apparatuses in which the electrons are emitted from a line-source filament and accelerated perpendicular to the filament in a continuous, linear neutron shielding foil, such as those available from Energy Sciences, Inc. under the trade name Electrocurtain. Ion radiation curing can be initiated by any means such as corotron. The liquid developers of the present invention have several advantages over liquid developers with non-curable liquid binders. For example, copies or prints made with liquid developers with the non-curable liquid binder often have an unpleasant odor caused by the residual binder remaining in the paper. However, copies or prints made with the liquid developers of the present invention have little or no odor because any liquid binder remaining on the print substrate after transfer is cured to a solid state. In addition, copiers or printers used in liquid development processes often emit solvent vapors as the non-curable liquid binder of the developers dries. Expensive and complex solvent capture systems are necessary to reduce solvent emissions from these solvents. Since the liquid hydrocarbon binders frequently used in conventional liquid developers tend to be chemically unreactive, the vapors of these hydrocarbons can only be captured by physical or mechanical means. In contrast, the curable liquid binders of the developers according to the present invention are more chemically reactive than the non-curable liquid hydrocarbons and the solvent emissions from the copiers or printers using these developers can be captured by simple, inexpensive chemical means such as the presence of a catalyst that hardens the liquid or by light radiation. In addition, waste disposal of the used developers from copiers and printers using conventional liquid developers represents an additional expense and inconvenience since the liquid binder must be disposed of by compatible organic solvent disposal methods. The liquid developers according to the present invention can, however, be cured to a solid so that the unused developer can be cured in the machine and disposed of as a solid. In addition, the majority of the liquid in curable liquid developers is carried out in the cured solid image. When non-curable liquid developers are used, the majority of the liquid developer is collected as waste. Copies or prints made from the liquid developers according to the present invention also exhibit excellent fixation to a support, particularly when the developed image is cured after it has been transferred to the support. The uncured liquid binder in the developed image penetrates the support and subsequent curing results in the image being thoroughly bonded to the paper or fabric fibers or to the support surface.

Specific embodiments of the present invention will now be described in more detail. These examples are intended to be illustrative and the invention is not limited to the materials, conditions or process parameters set forth in these embodiments. All parts and percentages are by weight unless otherwise indicated.

Example I

An electrophoretic liquid developer curable by ultraviolet radiation was prepared by first preparing a concentrated developer as generally described in Trout, U.S. Patent No. 4,707,429, column 11, Example 3, and then diluting the concentrate with UV curable monomers. Specifically, 35 parts by weight of Nucrel 699, a copolymer of ethylene (91 percent) and methacrylic acid (9 percent) having a melt index at 190°C of 100 and an acid number of 60, available from EI Du Pont de Nemours & Company, Wilmington, DE, 0.75 parts by weight of aluminum tristearate (a charging aid) available from Mathe Chemical Corporation, Lodi, NJ, 2.45 parts by weight of Sterling NS N774 carbon black, available from Cabot Corporation, Boston, MA, and 125 parts by weight of Isopar L, available from Exxon Corporation, were added to a Union Process Attritor, Union Process Company, Akron, OH. The ingredients were heated to 90ºC ± 10ºC and milled at a rotor speed of 230 rpm with 0.1875 inch (4.76 mm) diameter stainless steel balls. The average particle size per area was monitored during milling with a Horiba CAPA-500 centrifugal particle analyzer (the particle sizing procedure is described in US-A-4,707,429, column 4, lines 60 to 67). If the average particle size was less than 10 microns, the ingredients were cooled to room temperature while milling continued. The steel balls were removed after the mixture reached room temperature. Basic barium petronate, an oil-soluble petroleum sulfonate available from Sonneborn Division of Witco Chemical Corporation, New York, NV, was then added (96 milligrams per gram solids) to the mixture as a charge director. Subsequently, the concentrated mixture prepared according to the procedure of U.S. Patent 4,707,429 was diluted to two weight percent solids with a one to one mixture (weight) of decyl vinyl ether (Decave, available from International Flavors & Fragrances, Inc., New York, NY) and 1,4-bis[(vinyloxy)methyl)]cyclohexane (Rapi-Cure CHVE, available from GAF Corporation, Wayne, NJ). The resistivity of the developer was determined to be 4.3 x 10¹⁰ Ohm cm (at 5 volts, 5 hertz). The Isopar L from the concentrate remained in the liquid developer as a release agent.

Next, an electrostatic image was created on a sheet of dielectric coated paper (Versatec 4011 electrographic paper, available from Versatec, Santa Clara, CA) by (1) adhering a 4 to 5 inch piece of the dielectric paper, coated side excluded, to a 4 to 5 inch/0.5 inch aluminum block, (2) the aluminum plate connected to a high voltage power supply, Model 206 Pacific Precision Instruments, Concord, CA, (3) the power supply was set to +500 volts and turning on the power supply resulted in a bundle of resistive carbon fibers, Celioncelect 675, Celanese, Chatam, NJ, held in a thin plastic tube, and (4) an image was written on the dielectric paper with the charged fiber bundle used as a pen.

The electrostatic image was developed into a visible image by (1) mounting the aluminum plate with the image-wise charged dielectric paper attached to it on a second aluminum plate such that the void between the plates was 1 millimeter, (2) then connecting the power supply ground to the image-holding plate and the power supply lead to the opposite aluminum electrode, applying a potential of 100 volts (this electrical bias suppresses background development on the charged dielectric paper), (3) pouring about 5 milliliters of the electrophoretic liquid developer between the two plates, allowing the excess to drain off, and (4) separating the aluminum plates. A dark image with little background development corresponding to the recorded image was clearly visible.

The developed image was cured by (1) preparing a 0.67 weight percent solution of bis(tert-butylphenyl)iodonium hexafluoroarsenate prepared by the method described in Crivello and Lam, Macromolecules, 10 (6) 1307 (1977) (the entire disclosure of which is incorporated herein by reference) in a 2 to 1 mixture of decyl vinyl ether (Decave) and 1,4-bis[(vinyloxy)methyl)]cyclohexane (Rapi-Cure CHVE) and heating the solution to 90°C for 15 minutes, (2) spraying the starter solution using Crown spray equipment, Crown Industrial Products Company Hebron, IL, over the toned image and (3) the sprayed, toned image was passed through a Hanovia UV-6 curing station, Hanovia, Newark, NJ, with the UV lamp set at 300 watts and the feed conveyor at 20 feet per minute. The image was dry to the touch after curing and resisted abrasion when rubbed with a finger, demonstrating that addition of the UV initiator to the image and exposure to UV light cured the liquid to a black solid.

Example II

A UV-curable electrophoretic liquid developer was prepared as in Example I except that sterling carbon black was replaced with copper phthalocyanine, a cyan pigment available from BASF, Holland, MI. An electrostatic image was prepared on a dielectric paper according to the procedure described in Example 1 and the electrostatic image was prepared with this cyan liquid developer according to the procedure described in Example 1 except that the background bias was set at +50 volts. The developed image was cured to a cyan solid according to the procedure described in Example 1. The cured image was dry to the touch and resisted abrasion when rubbed with a finger. The resistivity of the developer (at 5 volts, 5 hertz) was 6.8 x 10¹⁰ ohm cm.

Example III

A UV-curable electrophoretic liquid developer was prepared as in Example 1 except that the sterling carbon black was replaced with Diarlylide Yellow, a yellow pigment available from Sun Chemical, Cincinnati, OH. An electrostatic image was formed on dielectric paper according to the procedure described in Example I and the electrostatic image was printed with this yellow liquid developer. according to the procedure described in Example 1. The developed image cured to a yellow solid according to the procedure described in Example 1. The image was dry to the touch and resisted abrasion when rubbed with a finger. The resistivity of the developer (at 5 volts, 5 hertz) was 4.1 x 10¹⁰ ohm cm.

Example IV

A UV-curable electrophoretic liquid developer was prepared by adding to a 4 ounce glass bottle 10 grams of Hostaperm Purple CM29701 pigment, available from BASF, Holland, MI, 90 grams of decyl vinyl ether (Decave), and 100 grams of 1/8 inch stainless steel granules and grinding the dispersion overnight. Five grams of the resulting concentrate was then diluted with 45 grams of dexyl vinyl ether (Decave) and 50 grams of 1,4-bis[(vinyloxy)methyl)]cyclohexane (Rapi-Cure CHVE). Subsequently, 1 gram of a 0.1 weight percent solution of a charge director, basic barium petronate in dodecane, was added to the diluted concentrate to prepare a developer. The resistivity of the developer (at 5 volts, 5 hertz) was 2.0 x 10¹¹ ohm cm. An electrostatic image was prepared by the procedure described in Example 1, except that the power supply was set to provide -500 volts to the coated surface of the dielectric paper. The electrostatic image was developed with this developer composition according to the procedure described in Example 1, except that the background bias was set to -100 volts. The developed image was cured to a magenta solid according to the procedure described in Example 1.

A second electrostatic image was formed under the same conditions and developed with the same developer except that the bias voltage was set at -150 volts. This magenta image was processed to a magenta solid using the procedure described in Example 1. cured. The image was dry to the touch and resisted abrasion when rubbed with a finger.

Example V

A UV-curable electrophoretic liquid developer was prepared according to the procedure described in Example IV, except that 2 grams of a 0.1 weight percent solution of basic barium petronate in dodecane was used. The resistivity of the developer (at 5 volts, 5 hertz) was 1.1 x 10¹¹ ohm cm. An electrostatic image was formed and developed with this developer composition as described in Example IV with the background magnetization voltage set at -100 volts, and the visible image was cured to a magenta solid according to the procedure described in Example I. The image was dry to the touch and resisted abrasion when rubbed with a finger.

Example VI

A UV-curable liquid developer for polarizable liquid development was prepared by (a) preparing a 30 weight percent solution of styrene-butyl methacrylate (equal molar) copolymer having a molecular weight of about 50,000 in butanediol divinyl ether (Rapi-Cure BDVE, available from GAF, Linden NJ), (b) mixing equal parts by weight of this polymer solution and the Hostaperm Pink dispersion described in Example IV, (c) preparing a UV initiator, di(isobutylphenyl)iodonium hexafluoroarsenate, as described by Crivello and Lam, Macromolecules, 10 (6) 1307, 1977, and (d) mixing 90.92 parts by weight of the polymer dispersion, 4.54 parts by weight of decyl vinyl ether (Decave), 4.54 parts by weight of butanediol divinyl ether (Rapi-Cure BDVE), and 0.20 parts by weight of the iodinium initiator. The resistivity of this polarizable developer was 7.7 x 10⁸ ohm cm and the viscosity, measured with a Brookfield viscometer LVT No. 2, Brookfield Engineering Laboratories, Stoughton, MA, measured at 60 revolutions per minute and at 22ºC, was 85 centipoise.

An electrostatic image was prepared on a sheet of dielectric paper as described in Example I, except that the potential applied to the carbon fibers was -400 volts. The electrostatic image was then developed into a visible image by applying the polarizable liquid developer to the electrostatic image with a Pamarco hand impregnator, Pamarco, Inc., Roselle, NJ, using a 150Q gravure and a 0.095 inch/20 millimeter/7 millimeter polyurethane doctor blade. The visible magenta image was cured by passing it through a Hanovia UV-6 curing station with the UV lamp set at 300 watts and the feeder running at 20 feet per minute. The image was dry to the touch and resisted abrasion when rubbed with a finger.

Example VII

A UV-curable liquid developer for polarizable liquid development was prepared by preparing a 40 weight percent solution of a styrene-butyl methacrylate (equal molar) copolymer having a molecular weight of about 50,000 in butanediol divinyl ether (Rapi-Cure BDVE), (b) grinding 37.5 grams of Mogul L carbon black, available from Cabot Corporation, Boston, MA, and 170 grams of decyl vinyl ether (Decave) in an 01S attritor at room temperature for 2 hours and then adding an additional 42.5 grams of decyl vinyl ether, and (c) combining 50 parts by weight of the carbon black dispersion with 10 parts by weight of decyl vinyl ether, 40 parts by weight of the polymer solution, 0.2 parts by weight of di(isobutylphenyl)iodonium hexafluoroarsenate. The viscosity of the polarizable developer thus formed was 145 centipoise and the resistivity was 1.5 x 10⁹ ohm cm.

An electrostatic image was formed, the electrostatic image was developed, and the developed image was cured as described in Example VI. The resulting black cured image was dry to the touch and resisted abrasion when rubbed with a finger.

Example VIII

Example VII was repeated except that the butanediol divinyl ether used was from BASF Corporation, Parsippany, NJ. The resistivity of the developer was the same but the viscosity was 160 centipoise. An electrostatic image was recorded and the image developed and cured as described in Example VI. The resulting black cured image was dry to the touch and resisted abrasion when rubbed with a finger.

Example IX

A curable photoelectrophoretic developer was prepared by adding about 7 weight percent of Locarno Red X-1686, 1-(4'-methyl-5'-chloroazobenzene-2'-sulfonic acid)-2-hydroxy-3-naphthalenecarboxylic acid, CI number 15865, available from American Cyanamide to a one to one mixture of dexyl vinyl ether (Decave) and 1,4-bis[(vinyloxy)methyl]cyclohexane (Rapi-Cure CHVE) and ball milling the resulting mixture for about 48 hours to reduce the particle size to an average diameter of less than 1 micrometer. A photoelectrophoretic imaging apparatus of the general type illustrated schematically in Fig. 1a of US-A-3,384,488 was used to test the developer, the developer being applied to the NESA glass support through which the exposure was carried out. The NESA glass surface was connected in series to a switch, a potential source and the conductive center of a roller having a coating of barite paper on its surface. The roller was about 2.5 inches in diameter and moved over the plate surface at about 1.5 cm per second. The plate used was about 3 inches square and was exposed to a light intensity of 1800 foot intensities. During imaging, a positive potential of about 2500 volts was applied to the core of the roller. The void between the barite paper surface and the NESA glass surface was about 1 mm. Exposure was carried out with a 3200°K lamp through a 0.30 neutral density step wedge filter, measuring the sensitivity of the suspension to white light, and then Wratton filters 29, 61 and 47b were placed individually over the light source in separate runs to measure the sensitivity of the dispersion to red, green and blue light, respectively. The images on the barite paper were coated with a starter solution and cured to a solid as in Example 1.

Comparison example A

20 parts by weight of the concentrated electrophoretic liquid developer described in Example I (before dilution to a 2 percent solids solution with decyl vinyl ether and 1,4-bis[(vinyloxy)methyl)]cyclohexane) was mixed with 40 parts by weight of a 30 weight percent solution of styrene-butyl methacrylate (equal molar) copolymer having a molecular weight of about 50,000 in decyl vinyl ether (Decave) and with 40 parts by weight of 1,4-bis[(vinyloxy)methyl)]cyclohexane (Rapi-Cure CHVE). The resistivity of this developer was 8 x 10¹¹ ohm cm, which is within the range of resistivities for developers used in electrophoretic development processes as described herein. The viscosity was 50 centipoise, which is outside the range of viscosities for developers used in the electrophoretic development processes described in the present invention. An electrostatic image was formed on a film of a dielectric paper and an attempt was made to develop the electrostatic image into a visible image as described in Example I. However, the image was unacceptable in that it was only partially formed. The high viscosity of the developer prevented uniform flow of developer through the development zone.

Comparison example B

To an electrophoretic developer prepared as described in Example I was added 0.02 wt% UV9310C, a di(p-dodecylphenyl)iodonum hexafluoroantimonate available from GE. The addition lowered the resistivity from 2.8 x 10¹⁰ ohm cm, which is within the range of resistivities for developers used in electrophoretic development processes as described herein, to 2.5 x 10⁹, which is outside this range. An electrostatic image was formed and an attempt was made to develop the electrostatic image into a visible image as described in Example I. However, no image was formed. The low resistivity of the liquid developer resulted in the electrostatic image being destroyed before the toner particles could develop a visible image.

Comparison example C

To 43.5 parts by weight of carbon black in a decyl vinyl ether dispersion prepared in Example VII were added 21.7 parts more decyl vinyl ether and 34.8 parts 1,4-bis[(vinyloxy)methyl)]cyclohexane. The resistivity of this developer was 2.6 x 10¹⁰ ohm cm and was within the range of resistivities for liquid developers used in polarizable liquid development processes as described herein, but the viscosity of the developer was 20 centipoise which is outside the range of viscosities for liquid developers. used in polarizable liquid development processes as described herein. An electrostatic image was formed on a dielectric paper and an attempt was made to develop the image as described in Example VI. However, the low viscosity of the developer resulted in the developer covering the dielectric paper and it was almost impossible to see the image and the image was unacceptable in that it was difficult to distinguish the image from the background.

The use of developers according to the present invention and as described above provides various advantages, including reducing or substantially eliminating solvent vapor emissions from copiers or printers using these liquid developers, reducing or substantially eliminating solvent vapor emissions from documents produced by liquid development processes using these liquid developers, and reducing solvent waste from liquid development equipment.

Claims (11)

1. A liquid developer comprising a colorant and a substantial amount of a curable liquid binder having a viscosity of not more than 500 millipascals (centipoise) and a resistivity of not less than about 10⁸ ohm cm, wherein at least about 80% by weight of the liquid component of the developer comprises the curable liquid. 2. The liquid developer of claim 1, wherein the curable liquid vehicle has a viscosity of not more than about 20 millipascals (centipoise) and a resistivity of not less than about 5 x 10⁹ ohm cm and a charge control agent, and wherein the colorant comprises colored particles capable of being charged and migrating through the liquid vehicle to develop an electrostatic latent image. 3. Liquid developer according to claim 1 or 2, wherein the curable liquid binder is selected from the group consisting of monoacrylates, monomethacrylates, epoxy resins, vinyl ethers, styrenes, indenes, vinyl acetals and mixtures thereof. 4. The liquid developer of claim 1, wherein the curable liquid binder has a viscosity of about 25 to about 500 millipascals (centipoise) and a resistivity of about 10⁸ to 10¹¹ ohm cm. 5. A liquid developer according to claim 1 or 4, wherein the curable liquid binder comprises molecules which radicals selected from the group consisting of cinnamic acid groups, fumaric acid groups, maleic acid groups, maleimide groups and mixtures thereof. 6. The liquid developer of claim 1, wherein the curable liquid binder has a viscosity of greater than 20 millipascals (centipoise) and a resistivity of not less than about 5 x 109 ohm cm, and wherein the colorant comprises photosensitive colored particles. 7. Liquid developer according to one of the preceding claims, wherein the developer also contains a starter. 8. Liquid developer according to one of the preceding claims, wherein the developer contains a release agent in an amount of up to about 20% by weight of the liquid binder. 9. A method of forming images which comprises forming an electrostatic latent image, contacting the latent image with a liquid developer according to any one of claims 1 to 3 or claims 7 or 8 when dependent on any one of claims 1 to 3, and curing the liquid binder remaining on the developed image after development. 10. A method of forming images according to claim 9, wherein the liquid developer is a liquid developer according to any of claims 1, 4 or 5 or claims 7 or 8 when dependent on any of claims 1, 4 or 5 and wherein the method further comprises: a. the provision of an application device with raised surfaces and lowered surfaces, b. applying the liquid developer to the recessed surfaces of the applicator, c. bringing the raised portions of the applicator into contact with an imaging member, thereby causing the latent image to attract the developer from the depressed portions of the applicator onto the latent image, thereby developing the latent image, and d. the hardening of the liquid binder that remains on the developed image. 11. A method of forming images according to claim 9, wherein the liquid developer is a liquid developer according to any of claims 1 or 6 or claims 7 or 8, when dependent on any of claims 1 or 6, and the method further comprises: a. introducing the liquid developer between at least two electrodes, b. exposing the developer between the electrodes to a light image while a potential is applied between the electrodes, thereby causing the formation of an image by depositing the suspended particles in imagewise configuration on the electrodes, and c. the hardening of the liquid binder that remains on the developed image.